Some processes that have multiple reaction steps require careful temperature control to produce optimal results. Examples of such processes include nucleic acid amplification reactions such as the polymerase chain reaction (PCR) and the ligase chain reaction (LCR).
Apparatuses have been developed which accurately control the temperature of reaction vessels that house amplification reactions. For example, thermal cyclers are used for DNA amplification and sequencing, and other applications. A conventional thermal cycler has a block, which holds a reaction mixture, or sample, and the temperature of the block varies over time. The temperature of the sample is monitored and a feedback signal is sent to a temperature controller to control the temperature of the block.
While conventional thermal cyclers are useful, a number of improvements could be made. For example, conventional thermal cyclers do not heat the samples in the most efficient way. When a thermal cycler is used to heat and cool a sample in a PCR reaction, it is desirable to heat and cool the sample as efficiently as possible to reduce the processing time and increase throughput. Also, a conventional thermal cycler uses a feedback loop to control the temperature of the sample. The temperature of the sample is sensed by a sensor, the temperature of the sample is calculated by the processor, and a signal is fed back to a controller which controls a heating element, which supplies heat to the block. The electronics and software that are used to provide the temperature feedback loop are often complex and increase the cost of the thermal cycler.
It would be desirable to provide for an improved apparatuses and methods for changing the temperatures of samples such as PCR reaction mixtures. Embodiments of the invention address these and other problems, individually and collectively.